Air cushion vehicle

ABSTRACT

An air cushion vehicle particularly useful for a drilling rig for oil wells and the like employed in arctic environments having open water, muskeg, ice, snow, and tundra is described. Means are also described for launching the air cushion vehicle from a ship and for preparing an arctic drilling site for the air cushion supported drilling rig. Means are provided on the bottom of the vehicle for preventing thawing of the frozen soil or ice beneath the vehicle as oil well drilling or workover operations are performed.

United States Patent Blurton et al.

AIR CUSHION VEHICLE Inventors: Leon C. Blurton, Brea, Calif.;

Saverio J. Cina, Brooklyn, NY.

Assignee: Global Marine Inc., Los Angeles,

Calif.

Filed: Apr. 1, 1971 Appl. No.: 130,462

Related US. Application Data Division of Ser. No. 12,778, Feb. 19, 1970, Pat. No. 3,693,729.

US. Cl 61/46.5, 62/243, 1 14/43, 175/5 Int. Cl. E2lb 7/12 Field of Search 61/46, 46.5, 36 A, 61/1, 50, 5; 175/5, 7; 166/DIG. 1; 62/243, 260, 240; 114/43; 180/116 References Cited- UNITED STATES PATENTS 5/1972 MCCUllOCl'l 175/5 [4 Jan.8, 1974 1,495,310 5/1924 Stromberg 61/46 3,675,430 7/1972 Haimila 61/46 FOREIGN PATENTS OR APPLICATIONS 1,144,201 2/1963 Germany 61/36 A Primary Examiner--Jacob Shapiro Attorney-Christie, Parker & Hale [5 7] ABSTRACT An air cushion vehicle particularly useful for a drilling rig for oil wells and the like employed in arctic environments having open water, muskeg, ice, snow, and tundra is described. Means are also described for launching the air cushion vehicle from a ship and for preparing an arctic drilling site for the air cushion supported drilling rig. Means areprovided on the bottom of the vehicle for preventing thawing of the frozen soil or ice beneath the vehicle as oil well drilling or workover operations are performed.

5 Claims, 4 Drawing Figures AIR CUSHION VEHICLE This is a division of patent application Ser. No. l2,778 now US. Pat. No. 3,693,729.

BACKGROUND In recent years there has been considerable interest and exploration for oil and gas reserves in artic regions, particularly in Alaska and northern Canada. In order to exploit these established oil and gas reserves, wells must be drilled under quite adverse conditions associated with the low temperatures of the arctic environment. Some of the areas of interest are in water in areas protected from the open sea, and these areas may be open in part of the year and frozen over in other parts of the year. In other regions, a substantially permanent layer of ice is encountered. Snow is found in some regions; and still others are what is known in the artic as muskeg, which is a boggy marsh unable to support ordinary land vehicles. Other areas of the arctic are tundra, which are open, treeless plains, having a blanket of organic material overlying a permafrost wherein a subsurface portion is permanently frozen and the surface portion is annually thawed to produce a mucky surface soil. Cutting roads through the insulating tundra exposes frozen soil beneath and destructive thawing may occur during the summer season.

When a drilling platform is placed on frozen soil or ice, heat from the oil well operations may cause thawing. This may cause permanent damage to delicate tundra or damage to the drilling rig. It is therefore desirable to provide a technique for performing oil well operations in frozen areas.

BRIEF SUMMARY OF THE INVENTION Therefore, there is provided in practice of this invention according to a preferred embodiment an air cushion vehicle including a chassis or platform for carrying a load such as a conventional assembled drilling rig and having means for cooling the bottom of the platform for maintaining a frozen surface. In use desired operations are performed on an oil well while maintaining a frozen surface beneath the platform by active refrigeration.

DRAWINGS These and many other features andadvantages of this invention will be appreciated as the same becomes better understood by reference to the following detailed description of a presently preferred embodiment when considered in connection with the accompanying drawings wherein:

FIG. 1 illustrates in perspective a drilling rig being transported on an air cushion vehicle constructed according to principles of this invention;

FIG. 2 is a side partial cross section of the apparatus of FIG. 1;

FIG. 3 is a top view of the apparatus of FIG. 1; and

FIG. 4 is a schematic view of a combined drilling rig and air cushion vehicle on a prepared drilling site.

DESCRIPTION FIG. 1 illustrates in perspective a combined drilling rig and air cushion vehicle constructed according to principles of this invention. As illustrated in this embodiment, a vehicle 12 is being towed by a conventional tractor 13 across an ice field or other arctic terrain. Surrounding the vehicle 12 is a flexible skirt 14 within which a large volume of air at increased pressure is pumped in order to lift the vehicle on a cushion of air trapped within the skirt. A shelter 16 on the main deck of the vehicle provides a habitable environment for workmen on the drill rig and protects drilling equipment from the severe arctic environment. A drilling tower 17 is mounted on the vehicle for handling the lengths of drill pipe employed in the conventional drilling and completion of an oil well or the like. The tower 17 in its drilling position (not shown in FIG. 1) is erect above the vehicle in the familiar posture of oil wells. During transport, however, in order to maintain the overall center of gravity of the vehicle as low as possible, and to lower the center of pressure of wind forces on the vehicle, the tower is folded to a lowered position. In a preferred arrangement, the tower has a lower section 18 and an upper section 19 which fold relative to each other as the lower section 18 folds down so that the transverse center of gravity of the tower is not greatly shifted between the raised and lowered positions.

FIGS. 2 and 3 illustrate in longitudinal cross section and top views, respectively, many of the construction details of the apparatus illustrated in perspective .in FIG. 1. In both of these views the shelter 16, illustrated in FIG. 1, is removed to show elements of the equipment which would otherwise be protected and hidden by the shelter. The main body of the vehicle comprises a platform or chassis 21 described in greater detail hereinafter. In a typical embodiment, the platform is about 64 feet long and about 46 feet wide, which provides sufficient room for the equipment required for drilling and completing an oil well.

In a typical arctic situation, a second somewhat similar vehicle would be stationed nearby for providing transport and storage of drill mud, cement, drill pipe, and the like. A third habitat vehicle having structures for housing crew members would also be stationed nearby. In most situations the transport and storage vehicle and the habitat vehicle would be located contiguous to the illustrated vehicle having the drill rig; however, on ice over water the other vehicles may be stationed as far away as 200 yards in order to permit the stresses induced by the weight of vehicles at the drilling location to be distributed through the layer of ice.

The total weight of the vehicle, icluding the drill rig and various expendables when set up for drilling, applies a weight of about 275 pounds per square foot which can safely be supported on a layer of ice about 5 feet thick. When the vehicle is traveling the footprint pressure is appreciably less due to decreased total weight because of the absence of expendables and a larger footprint area so that the traveling footprint pressure is about lbs per square foot (0.8 psi). which is approximately twice the footprint pressure of the usual air cushion vehicles presently employed at relatively high velocities.

Mounted on the platform or chassis 21 is a so-called sub-base 22, which provides a raised deck for workmen during drilling operations and which supports a portion of the equipment required for drilling operations, such as, for example, the approximately centrally located rotary table 23 conventionally employed in drilling operations. Mounted on the sub-base 22 are foundations 24 on which the lower segment 18 of the tower 17 is supported (the tower 17 is omitted from FIG. 3 for clarity).

The tower 17 is a substantially conventional folding tower such as available from the Lee C. Moore Company. Such a tower has a lower segment 18 pivotally mounted on a pair of foundations 24 so as to be pivotable between a lowered traveling position as seen in solid in FIG. 2, and a raised operational position as seen in phantom in FIG. 2. When the tower is in its raised position, legs 26 connected to a pair of the foundations 24, support the lower segment 18 in its raised position. The legs 26 are disconnected and pivoted out of the way or removed when the tower is folded down for transporting as in the position illustrated in solid in FIG. 2.

When the tower is folded down the upper segment 19 pivots about a pivot 27 so as to fold back across the lower segment 18 as controlled by a hydraulic actuator 28. The cylinder of the actuator 28 is connected to the lower segment 18 of the tower by a trunnion 29 and a piston is pivotally connected to the upper segment 19 by a bracket 31.

The otherwise conventional tower 17 is modified only by providing a plate 32 on one side of the upper tower section 19 so that the heavy pulley block and hook 33 can be snubbed over and lashed in place on the plate for transporting the tower in a lowered position. When the block 33 is in the lashed position as shown in FIG. 2 and the tower is folded, as illustrated in solid in FIG. 2, its overall transverse center of gravity is substantially directly below the center of gravity of the elevated tower.

A conventional pipe rack 34 is provided on the platform 21 for accepting lengths of drill pipe employed in drilling operations. A tank 36 for drilling mud is also provided on the platform, and in a position approximately opposite the center of gravity from the pipe rack 34, so that substantial amounts of pipe and mud in their respective receptacles do not grossly change the over all center of gravity of the platform. Other conventional well drilling equipment, such as, for example, pumps 37, an active mud tank 38, pipe set backs 39, and blow-out preventer control equipment 41 is also positioned on the main deck of the platform in a distribution that assures a vehicle center of gravity near its geometrical center.

t A conventional drill rig draw works 42 is positoned on the sub-base 22 for handling the cables commonly employed in oil well drilling. The draw works 42 are powered by a pair of prime movers 43 which are preferably diesal engines which power not only the draw works but also the pumps 37 and most other equipment commonly employed in drilling operations. The engines 43 are connected to the draw works and other equipment by way of a pair of clutches 44 so that they can be selectively connected and disconnected as desired. A second pair of clutches 46 are also connected to the diesel engines 43 so that the engines can be selectively connected to a pair of high volume lowpressure blowers 47. Each of the blowers 47 is connected to an air duct 48 which leads the air through the edge of the platform which is in the form of an outwardly extending flange 49 having intermittent braces 51 for weight support.

In operation, air is injected into the plenum 52 through the ducts 48 and the upper portion of the skirt is caused to billow outwardly under the urging of the increased air pressure. Webs 53 constrain the lower portion of the skirt and maintain it in the general configuration illustrated. Air passed downwardly from the plenum 52 through the spaces between the webs 53 which may, for example, be one or two feet apart, and escapes between the lower edges of the skirt and the ground 57. A portion of the air passed under the inner skirt 54 to increase the air pressure underneath the platform 21, and the principal portion of the air escapes beneath the outer skirt 14 into the environment. The air pressure built up within the inner skirt 54 and under the platform is substantially the same as the air pressure within the plenum 52, and as this builds up it applies a force against the bottom of the platform which serves to raise the platform.

In the preferred embodiment, there are means for engaging the ground, ice or other surface beneath the vehicle comprising a pair of sets of wheels 65 mounted on support bars 66 independently pivotally connected to the platform at pivots 67. The cylinder 68 of a hydraulic actuator is pivotally connected to the platform at a pivot 69, and the piston 71 of the actuator is connected to the support bar 66 adjacent the wheel 65 in each set. The hydraulic actuator is connected to a conventional pneumatic accumulator 72 for resiliently applying pressure to the hydraulic actuator. Thus, the wheels 65 can be extended to the position shown insolid in FIG. 2, or can be retracted to the position shown in phantom by varying the pressure in the pneumatic accumulator 72.

Just as in other drilling rigs a reasonable foundation for the platform must be prepared at the drilling site. If the drilling site is in open water, the vehicle is merely moored and floats at the site. Similarly, if the drilling site is in a muskeg bog, the platform is merely set on the surface of the bog and may sink some distance into the marshy ground without any problem whatsoever. On tundra, bulldozers may be employed for leveling and smoothing a site for the drilling platform, or if it is during the winter months, a technique similar to that suitable for smoothing and leveling an ice surface is preferred.

Such a technique is illustrated schematically in FIG. 4 wherein uneven ground is smoothed by erecting a cofferdam 79 surrounding the drilling site. The area witin the cofferdam is then flooded with water to a sufficient depth to cover any objectionable irregularities, and the water is then frozen to form a smooth level layer of ice 81. If a production well is to be maintained on the site, it may be desired to leave a subsurface cellar 82 in the region immediately below the tower 17. This provides a location for the blow-out preventer and other production equipment which may be installed on the well prior to departure of the drilling rig. This equipment is preferably installed in the cellar 82 so that the air cushion vehicle clears the equipment when it leaves the site. The cellar can be temporarily covered so that the air cushion is not lost as the skirt traverses the cellar. If the technique is employed on ice, the blow-out preventer is normally installed on the bed of the body of water beneath the ice. Also, in employing the technique on ice, the extent of the body of ice formed within the cofferdam 79 may extend a considerable distance beyond the drilling platform in order to raise the thickness of the ice to at least 5 feet for a sufficient distance to accommodate the stresses of the heavy drilling platform without breaking through the ice.

When the drilling platform is installed on ice, whether in its original condition or made by freezing a pond as illustrated in FIG. 4, care must be taken to avoid melting the ice due to the heat generated by the drilling rig. If the ice is melted, a problem may be encountered wherein the drilling rig freezes to the ice surface so that it cannot be readily moved to a new site. In order to avoid melting of the ice beneath the platform an insulating layer 83 is first laid over the ice prior to installing the platform in position. A suitable insulating material having low thermal conductivity and sufficient strength to bear footprint pressures of the order herein involved is readily available commericially in large slabs, which can be laid directly on the ice and cemerited together with hot asphalt or the like in order to form a continuous layer. Such arrangements are also employed in arctic airfields. Another suitable insulation involves a layer of styrofoam overlaid with two or three feet of gravel.

Rather than employing insulation over the ice there are also situations where it is desirable to provide artificial cooling to maintain the ice beneath the vehicle. Thus, as seen in the cutaway portion of FIG. 2 conventional refrigeration coils 84 are laid in good thermal contact with the bottom of the chassis 21 for cooling that surface. The coils 21 can be used for maintaining ice frozen beneath the platform and are also useful for intially forming a pad of ice to support the loaded weight of the platform when the ambient temperature is not sufficiently low to quickly freeze a sufficient layer of ice. The coils 21 can also be used for heating and deliberately thawing ice beneath the platform to prevent sticking when it is desired to move the platform to a new location.

What is claimed is:

1. An air cushion vehicle for use in locating and producing oil and gas in arctic areas, for example, comprising:

a platform;

depending flexible skirt means around the periphery of the platform for cooperation with a surface for minimizing air flow therebetween;

means for supplying air under pressure to below the platform within the skirt means for developing and maintaining at such location sufficient pressure to support at least a major portion of the platform and the contents thereof; and

means for cooling the bottom of the platform for maintaining a frozen surface upon which the platform may be supported. 2. Apparatus for performing operations at and in association with an oil or gas well in arctic areas comprismg:

a platform assembly including a buoyant hull having a substantially flat bottom,

an operations facility carried by the platform assembly operable to perform desired operations at and in association with an oil or gas well, and

heat transfer means carried by the platform assembly for cooling the hull bottom to a sufficient extent to freeze water beneath the hull.

3. A method of performing operations at and in association with an oil well, for example, at a land-based arctic location comprising the steps of:

placing an operations platform on the surface at said location; refrigerating the portions of the platform in contact with the surface sufficiently to prevent thawing thereof in the vicinity of the platform by reason of the presence of the platform or by reason of operations performed from the platform; and

performing desired operations at and in association with the well from the platform.

4. The method according to claim 3 including providing the platform with a flat bottom which engages the surface in performance of the placing step, and refrigerating the platform bottom sufficiently to freeze the surface below the platform bottom.

5. The method according to claim 3 including moving the platform to the location, and away from the location upon completion of operations, on a cushion of air. 

1. An air cushion vehicle for use in locating and producing oil and gas in arctic areas, for example, comprising: a platform; depending flexible skirt means around the periphery of the platform for cooperation with a surface for minimizing air flow therebetween; means for supplying air under pressure to below the platform within the skirt means for developing and maintaining at such location sufficient pressure to support at least a major portion of the platform and the contents thereof; and means for cooling the bottom of the platform for maintaining a frozen surface upon which the platform may be supported.
 2. Apparatus for performing operations at and in association with an oil or gas well in arctic areas comprising: a platform assembly including a buoyant hull having a substantially flat bottom, an operations facility carried by the platform assembly operable to perform desired operations at and in association with an oil or gas well, and heat transfer means carried by the platform assembly for cooling the hull bottom to a sufficient extent to freeze water beneath the hull.
 3. A method of performing operations at and in association with an oil well, for example, at a land-based arctic location comprising the steps of: placing an operations platform on the surface at said location; refrigerating the portions of the platform in contact with the surface sufficiently to prevent thawing thereof in the vicinity of the platform by reason of the presence of the platform or by reason of operations performed from the platform; and performing desired operations at and in association with the well from the platform.
 4. The method according to claim 3 including providing the platform with a flat bottom which engages the surface in performance of the placing step, and refrigerating the platform bottom sufficiently to freeze the surface below the platform bottom.
 5. The method according to claim 3 including moving the platform to the location, and away from the location upon completion of operations, on a cushion of air. 